diff --git a/chunky/src/java/se/llbit/chunky/main/Chunky.java b/chunky/src/java/se/llbit/chunky/main/Chunky.java
index e95590407..63de8da21 100644
--- a/chunky/src/java/se/llbit/chunky/main/Chunky.java
+++ b/chunky/src/java/se/llbit/chunky/main/Chunky.java
@@ -272,7 +272,7 @@ private void loadPlugins() {
       .filter(jarName -> !jarName.isEmpty())
       .map(jarName -> pluginsPath.resolve(jarName).toAbsolutePath().toFile())
       .map(PluginManager::parsePluginManifest)
-      .flatMap(o -> o.map(Stream::of).orElseGet(Stream::empty)) // replace with Optional::stream in java9+
+      .flatMap(Optional::stream)
       .collect(Collectors.toSet());
 
     // Load plugins
diff --git a/chunky/src/java/se/llbit/chunky/plugin/loader/JarPluginLoader.java b/chunky/src/java/se/llbit/chunky/plugin/loader/JarPluginLoader.java
index 1fe45de5a..50d76e8a8 100644
--- a/chunky/src/java/se/llbit/chunky/plugin/loader/JarPluginLoader.java
+++ b/chunky/src/java/se/llbit/chunky/plugin/loader/JarPluginLoader.java
@@ -23,7 +23,7 @@ public void load(BiConsumer<Plugin, PluginManifest> onLoad, PluginManifest plugi
     } catch (IOException | ClassNotFoundException e) {
       Log.error("Could not load the plugin", e);
     } catch (ClassCastException e) {
-      Log.error("Plugin main class has wrong type", e);
+      Log.error("Plugin main class has wrong type (must implement se.llbit.chunky.Plugin)", e);
     } catch (InstantiationException | IllegalAccessException | NoSuchMethodException | InvocationTargetException e) {
       Log.error("Could not create plugin instance", e);
     }